The invention relates to improvements in mechanism and method for assembling paper machine filled rolls, and particularly calender and embossing rolls of the type having a central mandrel with stacked fiber disks along the mandrel axis compressed thereon to provide a roll having a surface formed from the layers of disks on the mandrel.
Mandrels of these types are generally used in special finishing machines and frequently used on coated papers to produce special effects. One of these is a friction calender which consists of a mandrel having disks of paper or cotton filled material to form the roll and this filled roll is used in combination with one two highly polished chilled iron rolls which can be heated or cooled. The coated paper is passed between the rolls with the coated side next to the iron roll. The iron is revolved at a peripheral speed which exceeds that of the filled roll by 11/2 to 4 times and produces a polishing action on the coating.
The manufacture of filled rolls for this type of use or other calendering or embossing use involves sequentially sliding many disks of a relatively soft filled material over a roll mandrel while it is located vertically in a hydraulic press. The disks of filled material are in sheet form and are usually made of cotton fibers or cotton and wool fiber blends. A precise hole is die-cut or lathe bored in the center of the fill sheets so that there is an interference fit of 0.010" to 0.030" on the roll mandrel. A number of disks are placed on the shaft or mandrel and pressed under extreme high pressure to compact the material. This process is repeated a number of times until a complete shaft is filled through a given face length. Large rolls may require two weeks or more to complete the filling because the compression and compaction of the layers along the roll requires time for the axial force to take effect. For example, after a specified increment of fill material is placed on the roll mandrel, the material is subjected to pressure up to 12,000 psi for approximately 48 hours. This pressure and time serve to compact the fill material fibers together in a solid hard mass. Because the hydraulic press conventionally applies pressure from the bottom end of the roll mandrel, the bottom layer of fill material is subjected to the full pressure of the press. Each succeeding layer up from the bottom is subjected to a pressure which is reduced by an amount of frictional force between the fill material and roll mandrel for the layers below. Thus, the top layer is subjected to a pressure which is reduced by the total frictional force of all of the fill material below. This difference in pressure may cause a nonuniformity in the final compaction or density of the fill material. Also, if there are some layers of fill material which fit especially tight or have high friction with the roll mandrel, the material can hang-up while pressing and cause hard or soft rings in the finished roll.
When the compression assembly of the disks on the mandrel is completed, it is removed and milled or machined to a cylindrical smooth finished outer surface. When the completed assembled filled roll is used, the outer surface density or hardness is determined by the compaction of the disks placed on the mandrel and if nonuniform compaction has occurred, the hardness of the roll surface will be nonuniform, and thus the action of the roll on the paper web being processed through a calender will be nonuniform across the width of the sheet.
It is accordingly an object of the present invention to obtain a method and mechanism for assembling filled rolls which can achieve uniform density of compaction of the filler disks along the entire length of the roll mandrel.
A further object of the invention is to provide an improved method and mechanism of assembling a filled roll which reduces the time of manufacture and particularly reduces the compaction time required for each group of disks placed on the mandrel.
A still further object of the invention is to provide an improved method and mechanism for assembling filled rolls wherein better and more uniform control is attained over the degree of compaction between the disks and wherein problems during assembly such as hang-up of the disk with an especially tight fit are elimated.
A feature of the invention is to provide a hydraulic compaction device arranged with a vibration generator attached to the mandrel wherein the frequency, and/or amplitude of the vibration force applied to the mandrel can be varied to vibrate the partially filled and completely filled mandrel at its fundamental natural frequency or at any harmonic thereof while pressure is on the fill material. The vibration of the mandrel is monitored as to frequency and displacement to determine when a natural frequency or harmonic has been reached by adjusting the speed of the vibrational device. Change in harmonics is made during assembly so that nodal points which have little or no vibration can be changed in location along the length of the mandrel to avoid nonuniform compaction at or between the nodal points with the exciting frequency varied from harmonic to harmonic several times during the pressing period.
Other objects, advantages and feature, as well as equivalent structures and methods which are intended to be covered herein, will become apparent with the teaching of the principles of the invention in connection with the disclosure of the preferred embodiments thereof in the specification, claims, and drawings, in which: